If you are using another shell, the idea here is to make sure that QCAD looks in the current working directory for shared libraries (like the file 'libQtWebKit.so.4' you have mentioned). You may also export LD_LIBRARY_PATH or the equivalent thereof in your shell.

If I understand correctly, the qcad wrapper only forces "plastique" on systems with a kernel that advertises *Ubuntu*, but the theming issue also affects systems, that will not match this. Eg. mint, ubuntu with homegrown kernels etc.

The /black list/ could be amended, or turned into a /white list/ instead or plastique forced on all 64bit systems?

-style plastique should probably be forced on all 64bit systems using the Gnome Desktop (or certain versions thereof). Forcing it on all 64bit systems will leave the significant number of KDE desktop users with a non-consistent user interface experience. The start-up script also seems to require adjustments to make it Bash version 4 compatible.

This is with a Ubuntu 10.04. bash version is 4.1.5. The startupscript works flawlessly. Eg qcad -style motif tests OK. I also use it to run autostart scripts.

Curiously, here now pure qcad-bin (RC2) does not crash with the default theme, as it did half a year ago. This is not a gnome desktop, but an XFCE one, but the default theme, as seen from qtconfig, surely looks gtk-ish. I do not know, what has changed in the meantime. A quick google search turns out this post:
"http://www.qtcentre.org/threads/35092-QT-4-7-GdkPixbuf-WARNING-**-Bug!-loader-png-didn-t-set-an-error-on-failure"
Maybe the remedy therein helps: